The invention relates to a process for removing hydrogen sulfide from various "sour" industrial gases, and more particularly to such a process in which hydrogen sulfide is absorbed with a solid metal oxide absorbent. The invention further relates to an absorbent for use in such a process.
Hydrogen sulfide (H.sub.2 S)-containing gases become available in many industrial processes, such as oil refinery processes and coke-oven gas processes. Gases containing H.sub.2 S are, for example, the off-gases from a Claus reaction or unit, synthesis gases, natural gas, hydrocarbon process gases, such as hydrocarbon feeds for steam-reforming, hydrogen production, or production of synthesis gas by controlled oxidation.
Well known processes for removing H.sub.2 S from gas include wet processes in which a liquid absorbent, such as an alkanolamine solution, is used. Such wet processes are normally operated at temperatures between about 30.degree. C. and 50.degree. C. H.sub.2 S-containing gas usually contains water vapor as a major constituent. Wet H.sub.2 S removal processes require cooling of the gas, which causes the water vapor present in the gas to condense. This condensation implies a non-recoverable loss of heat, which in its turn results in a loss of thermal efficiency of the wet absorption processes. The loss of water in the gas is particularly regrettable, in the case of production of hydrogen or hydrogen-enriched synthesis gas, since a substantial amount of steam, obtained by water quenching of the gas, might be used in the downstream CO-shift section. If a synthesis gas process is integrated with a combined cycle power generation in a power station, the efficiency of the power station might be increased by increasing the temperature at which the H.sub.2 S removal is carried out.
To overcome the above disadvantages encountered with liquid absorbent systems, it has already been proposed to use oxides or hydroxides of metals for removing sulfur compounds from gases. Since these oxides are solid, the sulfur removal can take place at a much higher temperature than when using liquid absorbents. Metal oxide absorbents may be used for H.sub.2 S removal at temperatures of 300.degree. C. up to 600.degree. C. It has already been proposed to use zinc oxide for selectively absorbing H.sub.2 S at a temperature of from about 300.degree.-400.degree. C. The known absorbents based on zinc oxide, however, do not meet the requirements of high absorption capacity and high absorption velocity for H.sub.2 S, and do not possess the capability of frequent regeneration without a substantial impairment of the absorption capacity. To improve the absorption capacity, it has already been proposed to combine the zinc oxide with a suitable carrier material, such as silicon dioxide. It has, however, been found that such an addition of a carrier material has an adverse influence on the regenerability of spent absorbent.
It is an object of the present invention to provide a process for the removal of H.sub.2 S from gases, in which an absorbent based on zinc oxide is used which has superior absorption properties and good regeneration properties.